Anatomy of the Eye

Question 1

Surface anatomy of a closed eye?

Answer 1

1. eyebrows
2. eyelid - thinnest in the body
3. eyelashes/cilia
4. superior palpebral crease
5. inferior palpebral crease
6. nasojugal crease
   7 malar crease

Question 2

Surface anatomy of an open eye?

Answer 2

1. Palpebral fissure - the space you see between the eyelid margins
   - It measures 8-11mm on average.
2. lateral canthus - lateral corner of the eye
3. medial canthus - medial corner of the eye
4. At the medial canthus you have 2 small elevations called the plica semilunaris and the caruncle

Question 3

Anatomy of the lower eyelid?

Answer 3

Lower lid slightly everted so punctum visible
1. lacrimal punctum - tears are produced through these puncti found at the lid margins closest to the medial canthus
2. Mebomian orifices - secrete oil every time you blink, keeping aqueous content of tears from evaporating
3. cilia

Question 4

Bony anatomy of the orbit?

Answer 4

• Bony cavity represented as a pyramid of four walls that converge posteriorly.
• The volume in adults is about 30mls
• Eyeball occupies 1/5 of the space and Rest of space filled with peri orbital fat which offers a cushion
• Anterior limit of orbit cavity is called Orbital Septum (a barrier between eyelids and orbit)

Question 5

Bony anatomy roof of the orbit?

Answer 5

orbital plate of the frontal bone and the lesser wing of the sphenoid bone
Note important landmarks:
- the lacrimal gland fossa, which contains the orbital lobe of the lacrimal gland
- the fossa for the trochlea of the superior oblique tendon

Question 6

What is the periorbita?

Answer 6

• The periorbita is the periosteal covering of the orbital bones
• At the orbital apex, it fuses with the dura mater covering the optic nerve.
• Anteriorly, the periorbita is continuous with the orbital septum and the periosteum of the facial bones

Question 7

Bony lateral wall of the orbit?

Answer 7

composed of the zygomatic bone and the greater wing of the sphenoid bone
- Thickest and strongest wall

Question 8

Bony medial wall of the orbit?

Answer 8

LEMS
- composed of the orbital plate of the ethmoid bone, the lacrimal bone, the frontal process of the maxillary bone, and the lesser wing of the sphenoid bone
- located adjacent to the ethmoid and sphenoid sinuses and nasal cavity

Question 9

Thinnest walls of the orbit and their consequences?

Answer 9

the lamina papyracea
- between the orbit and the ethmoid sinuses
- These are the bones most frequently fractured as a result of indirect, or blowout, fractures
- Infections of the ethmoid sinuses may extend through the lamina papyracea to cause orbital cellulitis and proptosis.

Question 10

Bones of the orbital floor?

Answer 10

composed of the maxillary bone, palatine bone, zygomatic bone
- forms the roof of the maxillary sinus; does not extend to the orbital apex but instead ends at the pterygopalatine fossa: hence, it is the shortest of the orbital walls

Question 11

Walls of the orbital apex/optic canal?

Answer 11

1. Superior orbital fissure- btwn greater and lesser wings of spenoid
2. Inferior orbital fissure
3. Foramen rotundum transmits – CN 5 maxillary branch

Question 12

Anatomy of the globe?

Answer 12

1. Fibrous layer:
   - Cornea
   - Sclera
2. Vascular layer
   - Choroid coat
   - Ciliary Body (Ciliary muscle, Ciliary process)
   - Iris
3. Nervous layer
   - Retina

Question 13

What are the measurements of the eye?

Answer 13

• a sphere 2.5 cm in diameter with a volume of 6.5 ml.
• the average axial length of the globe is 24 mm (range 21–26 mm)
• The diameter is 23 mm and the horizontal length approximately 23.5 mm.

Question 14

Describe the optic nerve?

Answer 14

• Formed by convergence of ganglion cell axons at the optic disc (beginning of nerve)
• Composed of 1.2 mil axons
• Foveal/macular fibres constitute ≈ 90% of all axons leaving the eye

Question 15

Describe the outer layer of the eye?

Answer 15

• The outer later has a smaller one anteriorly, the cornea, that has a greater curvature than the sclera, which constitute the large sphere
• The cornea forms one-sixth of the circumference of the globe and has a radius of 7.8 mm; the remaining sclera has radius of 11.5

Question 16

Describe the cornea?

Answer 16

• has a greater curvature than the sclera, which constitute the large sphere
• It is transparent and makes 1/6 of the globe
• It’s about 12mm horizontally and 11 mm vertically
• avascular
• It’s bordered by the limbus

Question 17

5 layers of the cornea?

Answer 17

1. epithelium
2. Bowman’s layer
3. Stroma
4. Descemet’s membrane
5. endothelium
   - epithelium + stroma (thickest layer of the cornea)

Question 18

Describe the sclera?

Answer 18

• It’s opaque and tough.
• It contributes 5/6 of the outermost coat hence borders with limbus.
• the limbus links cornea and sclera

Question 19

Parts of the sclera?

Answer 19

1. Covered by loose CT
   - conjunctiva
2. Tenon capsule
   - is an envelope of elastic connective tissue deep to conj.
   - The Tenon capsule is the cavity within which the globe moves.
3. it divided into these anatomical parts;
   - Palpebral
   - Bulbar
   - Forniceal

Question 20

Describe the middle layer of the eye?

Answer 20

• It is also known with the following names: uvea or uveal tract, vascular coat or nourishment layer.
• Its made up of Iris, Ciliary Body, Choroid.

Question 21

Describe the pupil?

Answer 21

• created by iris
• Muscles = sphincter and dilator to control the amount of light that enters the pupil

Question 22

Ciliary body parts?

Answer 22

1. pars plana
2. pars plicata

Question 23

Describe the muscles of the iris in various forms of light?

Answer 23

1. bright light - circular muscles contract reducing the size of the pupil
2. dim light - radial muscles contract enlarging the size of the pupil

Question 24

Describe the inner layer?

Answer 24

• does not go all the way anteriorly
• retina has 10 layers

Question 25

Describe the retina?

Answer 25

- retina made of Rods and cones - Cones concentrated at fovea - 6 million cones. 120 million rods - has a macula and optic disc

Question 26

What is the optic disc?

Answer 26

- Circular to slightly oval structure measures 1.5 mm in diameter - Has a central depression called physiological cup - Where the Opthalmic nerve CN II connects to the retina - The main blood vessels go through it - Known as the blind spot because it does not contain rods and cones (photoreceptors) and cannot detect light

Question 27

What is the macula?

Answer 27

small, yellowish, oval-shaped area at the center of the retina responsible for sharp, clear central vision and colour perception

Question 28

Muscles of the eyelid?

Answer 28

1. orbicularis oculi - Supplied by CN 7 - Closes the eyelid 2. levator palpabrae superioris - closes the eye - Innervated by superior division of CN 3 - deeper

Question 29

Parts of orbicularis oculi?

Answer 29

1. orbital 2. preseptal 3. pretarsal

Question 30

Name the extraocular muscles?

Answer 30

1. superior oblique 2. superior rectus 3. medial rectus 4. lateral rectus 5. inferior rectus 6. inferior oblique

Question 31

Origin and insertions of extraocular muscles?

Answer 31

- All EOMs with exception of Inferior Oblique arise from the apex of the orbit - Tendinous Ring of Zinn - the inferior Oblique originates from the medial wall of the orbit: It is the shortest EOM Muscle. - The Superior Oblique Muscle before it inserts on the globe it passes through a trochlear pulley on the medial wall of the orbit.; It is the longest EOM - However, all the six EOMs insert on the globe.

Question 32

Blood supply to the globe?

Answer 32

1. The ophthalmic artery branches from the internal carotid artery just as it emerges from the cavernous sinus. - Gives of branches to the extraocular muscles 2. central retinal artery - to the optic nerve and retina 3. posterior ciliary arteries - long to the anterior segment and short to the choroid

Question 33

Main arterial blood supply of the globe?

Answer 33

Ophthalmic Arterial System - Central Retinal artery

Question 34

Posterior Ciliary arterial blood supply to the globe?

Answer 34

1. Long posterior ciliary artery 2. Short posterior ciliary artery - Approximately 20 short posterior ciliary arteries and 10 short posterior ciliary nerves enter the globe in a ring around the optic nerve - The posterior ciliary vessels supply the whole uveal tract, the sclera, the margin of the cornea, and the adjacent conjunctiva

Question 35

Anterior ciliary artery blood supply to the globe?

Answer 35

- The anterior ciliary arteries also arise from the ophthalmic artery and usually supply (in pairs) the superior, medial, and inferior rectus muscles - A single anterior ciliary vessel enters the lateral rectus muscle from the lacrimal artery

Question 36

Venous drainage of the globe?

Answer 36

1. The vortex veins 2. The central retinal veins 3. The drainage through the cavernous sinus

Question 37

Nerve supply to globe?

Answer 37

SO4LR6R3 1. superior oblique - trochlear 2. lateral rectus - abducens 3. superior rectus, medial rectus, inferior rectus, superior palpebral levator muscle 4. CN V - sensory innervation to orbital contents - Sensory portion also subserves greater part of scalp, forehead, face, eyelids, eye including cornea, lacrimal gland, EOM. Note: CN 5 - Involved in herpes zoster ophthalmicus

Question 38

Lymphatic drainage of the eye?

Answer 38

- Lymphatic vessels are present in the eyelids and conjunctiva, but neither lymphatic vessels nor nodes are present in the orbit - Lymphatic drainage from the eyelids parallels the course of the veins

Question 39

2 groups of lymphatics in the eye?

Answer 39

1. a medial group that drains into the submandibular lymph nodes 2. a lateral group that drains into the superficial preauricular lymph nodes

Question 40

2 systems of the lacrimal system?

Answer 40

1. secretory system 2. excretory system

Question 41

Secretory system of the lacrimal system?

Answer 41

1. Lacrimal gland 2. Accessory Lacrimal glands - Gland of Wolfring - Gland of Krause 3. Meibomian gland, Goblet Cells

Question 42

Excretory system?

Answer 42

1. Puncta 2. canaliculus 3. Common canaliculus 4. Lacrimal sac 5. Nasal-lacrimal duct

Question 43

Function of the lacrimal system?

Answer 43

production and drainage of tears